The RAF was monitoring events on the ground at Abu Kamal in eastern Syria on Tuesday May 9, and spotted a large crowd of civilians gathering in one of the town’s main streets, the MoD says. When it realized an execution was about to occur, it struck an IS sentry with a hellfire missile fired from a Reaper drone.

“When a van then unloaded two shackled prisoners in front of the crowd, it became clear that Daesh [IS] were organizing a public execution,” an MoD spokesperson told the Guardian.

“Given the large number of civilians present, the Reaper’s crew could not target directly the Daesh fighters about to carry out the murders. However, two armed extremists were stationed as sentries on the roof of a building overlooking the scene.

“A Hellfire missile was fired immediately, and scored a direct hit which not only killed one of the sentries, but also brought the execution to an immediate halt, as the Daesh fighters fled the scene, and the crowds of civilians dispersed.”